1. Field of the Invention
The present invention relates to a recording sheet suitable for use in an ink jet recording process and particularly to a sheet in which the images and characters recorded thereon can be clearly observed by both reflected and transmitted light.
2. Description of the Prior Art
Recently, ink jet recording processes have become extremely popular in the data processing art and one of their most frequent applications is with computer print outs. Ink jet recording is so well accepted because it is not accompanied by large amounts of noise and it is capable of printing at high speeds. In addition, the quality of the images produced in a multicolor ink jet process is comparable to the images produced in a conventional multicolor printing process and they equal the quality of color photographic images in terms of the size of images. Regarding expense, copies can be made at a lower price in the multicolor ink jet process as compared to the multicolor printing process if the number of copies is few, to say nothing of the color photographic process.
Attempts have been made to use the records obtained by the ink jet process in exhibitions without restricting the use of the ink jet process to only recording purpose. There are basically two forms of display: a so-called reflection form in which images formed on a sheet such as paper or the like are observed from the image side and a so-called transmission form in which a light source is placed behind the image bearing sheet and the images are observed from the image side by light transmitted through the sheet. It has been known that images can be more clearly seen by using the latter form of observation under particular conditions such as in a dark room, in the open air at night and the like. As a prevailing example of the latter display form, mention may be made of the case that a number of fluorescent lamps are arranged behind a large size transparent positive photograph and fixed on an interior wall of a room.
The display form is selected depending upon the circumstances under which exhibition is to take place. However, if images of good quality could be observed in each instance, images on one sheet could be applied in both reflection and transmission displays. Such display sheet is well suited for image observation in places in which the amount of light varies over a broad range. However, experience has shown that it is very difficult to prepare on one sheet images which have desirable color density and which can be clearly observed in both reflection and transmission displays. That is to say, when images of the type which can be observed with moderate density by reflection are observed by means of transmitted light, they are so obscure and have such low density that they cannot be seen. On the other hand, in case of observing images best suited for the transmission forms by means of reflected light, the images have such high color density and they are so dark that they cannot be employed as exhibits.
It has been found that the fact that the dye images exist only as a very shallow layer in the vicinity of the surface of a sheet, as observed in the case of multicolor prints and color photographs, is the reason that images of moderate density cannot be observed on one common sheet by both reflection and transmission at the same time. It has also been found that it is possible to observe images clearly on one common sheet by both reflection and transmission forms when the image is formed on a sheet possessing certain, particular properties in accordance with an ink jet process, such that the image is produced in such a manner that the dye images are formed in a desired depth. The above-described particular properties include moderate opacity and moderate ink absorbing power.